1. Background
A growing market has developed for tools and systems that track humans and other bodies at rest and in motion. The applications for such systems vary considerably, and include such areas as the creation of computer-generated and graphical animations, the analysis of human-computer interaction, the assessment of performance athletics and other biomechanics activities, and the evaluation of workplace and other activities for general ergonomical fitness.
The possible sample uses for a body-tracking system are wide and varied. For example, a user interested in creating a realistic computer animation of a gymnast might be interested in tracking the full-body movements of the gymnast during a brief tumbling run characterized by high-velocity, high-acceleration activity. A second sample user might instead be interested in measuring the upper-body movements of a typical clerical worker over a full workday, in order to assess the role of various activities in causing repetitive stress injury. A third sample user might wish to record the motions of a high-performance skier or snowboarder over a mile-long section of mountain in order to study and possibly improve his or her technique.
The most general functional requirement of a body-tracking (or motion-capture) device is that it accurately and reliably measure and report the configuration of the various articulating members (limbs) of the body over a particular duration of interest. In order to be most useful, however, a motion-capture device must also satisfy additional criteria. It must be sufficiently lightweight and unencumbering to allow the free performance of the activity being measured. (A system that prevents an athlete or performer from acting naturally, either due to the addition of weight, to an impeding of balance and flexibility, or to the presence of other physical constraints is clearly of lessened utility as a motion-capture device). It must also allow for a performance space appropriate to the motion being measured, i.e., it must allow the user the freedom to move through space as needed to complete the activity being measured.
Various contributions to the prior art have addressed themselves to the general problem of motion capture. Electromagnetic (E/M) tracking systems, such as those manufactured by Polhemus and Ascension, use multiple elements consisting of three orthogonally wound coils. At least one such element is designated as a transmitter, and at least one such element is designated as a receiver. By energizing, in turn, the coils in a transmitter element, and measuring the signal induced in the receiver elements(s), the relative position of the transmitter and receiver element(s) can be calculated. Such E/M tracking systems are sensitive to the presence of metal in the close surroundings and, in addition, have a workspace limited by the requirement that the receiver(s) remain within several feet of their corresponding transmitter. Another disadvantage of E/M technology is that it typically includes lag time which renders the position data non-real time.
As with E/M position sensing technology, ultrasonic (US) and infrared (IR) position sensing technologies do not require a direct tether between the hand and monitor. US and IR technologies have the disadvantage, however, that they both require direct line of sight. Thus, when one hand passes in front of the other, the position signal can be lost. Additionally, US technology, in particular, is very sensitive to ambient acoustic noise. Both technologies can introduce lag time, again rendering the position data non-real time.
Another example of a prior art solution to the problem of motion capture is a passive, optically-based body-tracking system, such as that produced by Motion Analysis. In such a system, multiple reflective markers are attached to the surface of the limbs of interest, such that these markers are placed on either side of the articulating joints. Multiple cameras record the positions of these markers over time, and this marker position data is used to extract (via xe2x80x9cinverse kinematicsxe2x80x9d) the corresponding configurations of the various limbs and joints of interest. Such optical tracking systems have an inherent workspace limitation that comes from the need to use cameras, namely that the user of the system is limited to the relatively small workspace that is both visible to the cameras and in focus. Tracking problems occur when markers become occluded, since data cannot be recorded. In addition, such a system requires a non-trivial amount of post-processing of the data; while it is expected that computing power and cost efficiency will continue to increase, optical systems still do not deliver on-the-spot, xe2x80x9creal-timexe2x80x9d data.
Still another example of a prior art solution is an active, optically-based body-tracking system. Such a system is conceptually similar to the passive system described above, but with several differences. The markers in such a system typically actively emit light, instead of being simple, passive reflectors. This allows the controlling software to energize each of the markers in turn, and if properly synchronized with the computer doing the data analysis, can help prevent problems that occur when the control software loses track of xe2x80x9cwhich marker is which.xe2x80x9d Otherwise, the workspace, marker-occlusion, and post-processing shortcomings of such active optical systems are similar to that of the passive ones.
A Toronto-based company, Vivid Group, uses camera-based technology called Mandela to monitor human motion without requiring the user to wear any special devices. The system, however, only tracks body movements in two dimensions (2D). Most motion capture (MC) systems require the user to wear some form of element that either is a sensor itself, or is one component of a sensing system where other components are located off the user.
Still another example of a prior art solution is a theoretical simulation of the desired motion. By building a kinematic model of a human, attributing that model with realistic masses, rotational interias and other properties, and specifying all relevant initial-condition and boundary constraints, it is theoretically possible to solve the dynamic equations of motion for a complex body. Once a solution has been generated, such information could be used to create graphical animations or other imagery. There are several drawbacks, however. For example, such algorithmic solutions to motion capture are just now in their infancy and can be applied only in the most limited and constrained of activities. Also for example, the human brain is very good at detecting xe2x80x9cincorrectxe2x80x9d motion, so the performance demands on such a theoretical simulation will be very exacting. Also for examples such a system does not help at all with the problem of measuring the motion of living humans and is of little utility in biomechanics and ergonomic applications.
There still remains a need for a position-sensing device which is accurate, insensitive to environmental influences, has little lag time and has high data rates.
2. Relevant Literature
U.S. Pat. No. 5,676,157, xe2x80x9cDetermination of Kinematically Constrained Multi-Articulated Structuresxe2x80x9d, J. F. Kramer, describes kinematically constrained multi-articulated structures.
A general overview of the inventive structure and method is now provided. The subject invention provides improvements, enhancements, and additional patentable subject matter to the prior provisional patent application numbers U.S. Patent Application Serial No. 60/044,495, filed Apr. 21, 1997, and No. 60/054,745, filed Aug. 4, 1997, which provisional applications are incorporated herein in their entireties. In particular, the subject invention provides new shoulder- and hip-sensing structures and techniques. In particular for each shoulder sensor assembly, this new structure and technique employs five long, thin, flexible strain-sensing goniometers to measure the overall angle of one or more contiguous parallel-axis revolute joint sets. The shoulder-sensing assembly is able to measure the angle of the humerus relative to a fixed point on the back. A hip-sensing assembly similar in construction to the shoulder sensor is able to measure the angle of the femur relative to a fixed point on the pelvis. Multiple parallel-axis joints provide extensibility, such as a prismatic joint function, in addition to providing the overall angle between the distal links of the two most extreme joints. In contrast, typical prismatic joints comprised of one cylinder sliding inside another often exhibit sliding friction and frequently bind if the forces between the cylinders are off axis. By building a xe2x80x9cprismatic jointxe2x80x9d from revolute joints, binding can be eliminated and resistance to movement greatly reduced.
As provided in this and the afore described provisional patent applications, a very thin linkage with small diameter joints may be fabricated, where flat, flexible bend sensors are used to measure the arc subtended by the distal links. To hold the bend sensors against the linkage structure, special guides may be used. These guides provide a channel in which each sensor slides against its associated linkage as a structural joint is rotated. The guides also limit the range of motion of the neighboring joints. One or more guides may be fastened to a link. The guides for adjacent links are typically designed to come into contact at a pre-determined joint angle, thus limiting joint range by preventing the joint from bending further. The guides may be fastened to the intended link in any convenient manner. In particular, the guides may have clips which allow them to snap around the intended link.
By way of overview, the Virtual Technologies"" goniometer-based body-tracking device, equivalently referred to as the Range-Of-Motion Suit (ROMS) or the CyberSuit(copyright), uses a bend-sensing technology to measure five degrees of freedom of the leg and foot, and six degrees of freedom of the arm and wrist. The degrees of freedom (DOF) measured by one embodiment of the present structure includes: ankle flexion, knee flexion, hip abduction, hip flexion, hip rotation, wrist flexion, wrist abduction, elbow flexion, shoulder flexion, shoulder abduction, and shoulder rotation. The present design directly extends to measurement of flexion, abduction and rotation of the lumbar and thoracic regions of the back, in addition to the neck. Means are also provided for measuring forearm rotation.
The CyberSuit measurement system includes a Lower Extremity Assembly (LEA), an Upper Extremity Assembly (UEA), a Waist Pack Assembly (WPA), and VirtualBody(copyright) graphical body-simulation software. The LEA and UEA are Lycra(copyright)-based garments with pockets and fixtures for removable sensor assemblies. The WPA is a belt-mounted pack that contains all the instrumentation electronics for data collection and logging. VirtualBody software contains utilities for user calibration, graphical body model, and real-time data acquisition via the WPA. A hand-held controller with LCD and six buttons serves as an optional user interface.
An overview of the CyberSuit is now described. The patented Virtual Technologies, Inc. (Palo Alto, Calif.) resistive bend sensor (goniometer) (Kramer, et al, U.S. Pat. Nos. 5,047,952 and 5,280,265, which are hereby incorporated by reference) is the basis of the angle-sensing technology used in the CyberSuit. Sensors similar to those used in the Virtual Technologies CyberGlove product have been incorporated into innovative multisensor assemblies to accommodate the larger joints of the knee, ankle, elbow and wrist, and the complex ball and socket joints of the shoulder and hip. Mechanically, the sensors are thin strips approximately 0.01xe2x80x3 thick, 0.20xe2x80x3 wide (minor axis), and variable length (major axis). The sensor measures the angle between the tangents at its endpoints when the sensor assembly experiences pure bending about the minor axis. The CyberSuit incorporates assemblies which use these sensors to accurately measure 1, 2 or 3 degrees of freedom, as appropriate, at each joint. Both the LEA and the UEA incorporate two types of sensor assemblies, a 1-DOF assembly used on the ankle, knee, and elbow, and a 3-DOF assembly used on the hip and shoulder. The UEA also includes a 2-DOF sensor assembly, used on the wrist.
The CyberSuit incorporates the sensors in a Lycra suit with an embedded wiring harness, sensor pockets, connector pockets, and base plates. The sensor pockets hold flat sensors used in 1-DOF and 2-DOF assemblies, which measure angles directly on the body. The base plates serve as fixation points for mechanical assemblies consisting of multiple, light, rigid links. The sensors are attached to the linkages in such a way that they measure three degrees of freedom between relevant major bones while bypassing intermediary body segments.
The inventive structure and method incorporate numerous design details and innovative elements, some of which are summarized below. Other inventive structures, methods, and elements are described in the detailed description.
One innovative element, the 3-DOF assemblies, include the above-mentioned mechanical linkages, with attached sensors, and the base plate, fabric, and strap configuration which secures the linkage to the body segments between which the relative orientation is being measured. The linkage assemblies typically consist of at least three segments, each of which contains many individual links but bends only in one plane. This compound planar series of linkages measures the angle between linkage endpoints while permitting some translation of one end-link with respect to the other. Using several of these linkage segments achieves X-Y-Z translation and full range of motion for a body joint. The linkage endpoints mirror the orientation of one bone with respect to another so the sensors effectively measure the particular bone-to-bone angular orientation. The base plates are held to the suit in fabric pockets including straps which can be adjusted for each user in such a way as to maintain a known fixed orientation between the linkage endpoint and the bones being measured. This linkage design and application allows for user-independent calibration of the linkage assemblies themselves. Due to the details of the linkage and joint geometries, the design employs a method of attaching the sensors to the linkages which captures and protects the sensor, maintains a fixed tangency with the linkage endpoints, and accommodates length changes which occur throughout the full joint range of motion. The use of multi-link planar segments allows significant translation without orientation change, which permits measurement over a full range of motion for a wide range of users. The link lengths are adjustable for different users of more variant body types.
Another innovative element are the 2-DOF assemblies. The sensor configuration used on the wrist is designed to handle the special case of a joint in which two degrees of freedom are measured and there is a limited range of motion. This design includes fan-shaped pockets and corresponding tabbed bend sensor guides which physically decouple the two degrees of freedom being measured and allow each one to be accurately measured with a single linear 1-DOF sensor.
The 1-DOF assemblies include 1-DOF joints which are directly measured with a sensor assembly encased in a flat fabric pocket sewn to the Lycra material of the suit. The assembly consists of three layers: bottom and top guide layers of smooth plastic and a middle sensor layer. The guides are designed to protect and enclose the sensor while allowing free sliding within the pocket and relative sliding between the sections to prevent buckling. The guide and pocket are also designed to maintain sensor endpoint tangency with the body part being measured. The design also allows the sensors to be used by users with different limb lengths and joint geometries and to accommodate these variations without adjustment. The sensor layer can consist of one long sensor or multiple sensors of various lengths which are electrically cascaded in series. These guides include devices to maintain endpoint tangency between consecutive segments while allowing sliding.